Television film projection with synchronized discharge lamp



Se t. 27, 1949. D. E. NORGAARD TELEVISION FILM PROJECTION WITH SYNCHRONIZED DISCHARGE LAMP Flled March 15, 1946 l I l l I I 3 W R d w M w mw & a O mu m t o o c n N mm 8 E A V 6 Q; W n h .t L I m L o y D b ww -ww .1:$W.II I \F I I I I I A a W I; I um. ,mmmmwl 13? 3E Mi 1 Patented Sept. 27, 1949 TELEVISION FILM PROJECTION WITH SYNCHRONIZED DISCHARGE LAMP Donald E. Norgaard, Scotia, N. Y assignor to General Electric Company, a corporation of New York Application March 13, 1946, Serial No. 654,133

4 Claims. (01. 178-72) My invention relates to motion picture projection systems and more particularly to television systems for transmitting pictures from motion picture films.

One of the objects of my invention is to provide improved illumination of the motion picture film and cathode ray camera tube in such systems.

A further object of my invention is to secure this advantage while obviating the use of shutters for control of the light.

A further object of my invention is to provide improved means to produce intense pulses of light for transmission through the film to the camera tube in desired synchronous relation with the operation of the deflection system of the camera tube.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention and Fig. 2 represents a detail thereof.

Referring to Fig. 1 of the drawing, I have illustrated therein a motion picture projection appa- P ratus in which a motion picture film is, during operation of the apparatus, wound from a reel l onto a reel 2 passing in its travel between the rolls, an aperture 3 where light is transmitted through it by means-f a, lamp 4. The film is driven by means of sprockets 5 and 6 and the intermittent drive mechanism 1. The sprockets 5 and 6 and the intermittent drive mechanism 1 are connected for operation by means of a synchronous motor 8 as indicated by the dash lines 9. The intermittent drive mechanism 1 comprises a sprocket l2 which operates intermittently to pull the film in step by step fashion through pressure shoes l3 and it. These pressure shoes each comprise a pair of members on opposite sides of the film to guide it across the aperture 3. Preferably, one of each of these pairs of members is fixed in position and the other spring pressed against the film to produce a certain amount of friction thereon, thereby to keep the film taut across the aperture 3 and to hold it into position when the film is stopped. This mechanism and the intermittent drive mechanism 1, l2 are conventional in motion picture apparatus and require no further explanation.

Light from the lamp 4 first passes through appropriate condensing lenses l5, thence through the film and aperture 3 and further lenses it to, in the equipment illustrated, the photo-sensitive area I! of a televisioncamera tube l8. All of the apparatus between the lamp 4 and the camera tube is the conventional apparatus commonly used in motion picture television projection equipment and differs therefrom only in that the shutters commonly used are omitted. V

The camera tubel8 may be the usual cathode ray type commonly referred to as iconoscope. The photo-sensitive surface l1 comprises elemental areas which become electrically charged when light falls thereon to an extent dependent on the intensity of the light. When the cathode ray of the tube impinges on the elemental areas, such areas discharge producing a current in the resistance IQ of intensity dependent upon the degree of light to which the elemental area is subjected. The voltage from this resistance is may be supplied to the conventional television transmitter for transmission in the usual well known way.

The cathode ray of the camera tube I8 is provided with horizontal deflection coils 20, which are supplied with essentially saw tooth current waveforms from horizontal deflection generator 22. The cathode ray is also deflected with vertical deflection coils 23 which are supplied with essentially saw-tooth current wave forms produced in a vertical deflection generator 24. The vertical deflection generator preferably produces a wave having a frequency of cycles per second and is synchronized from a pulse generator 25. The horizontal sweep generator 22 operates at a much higher frequency, as for example 15,750 cycles per second, and is likewise controlled in frequency and in its time phase relation by the synchronizing pulse generator 25. This synchronizing pulse generator 25 is supplied with synchronizing voltage over a conductor 26 from a (SO-cycle, 3phase source 2! from which the synchronous motor 8 is supplied thereby to synchronize the sweep voltages supplied to the cathode ray device l8 with the intermittent motion of the film across the aperture 3.

At the left-hand portion of the drawing are shown circuits for energizing the lamp 4 to project intense pulses of light through the aperture 3 during the intervals when the film is stationary therein. This apparatus, in the form illustrated,

; 7 comprises a multi-wibrator 21 and vacuum tubes duration equal to about of the period or the pulse wave.

These pulses are supplied tdj thefgi id 3d of the multi-vibrator 21. This niultivibrator comprises a pair of electron discharge devices and 36, each having an anode, a cathode and-a -control electrode. The cathodes of the discharge,

devices are connected together and through a resistance. 31 toa pointjts v betvveen two sources 39"and 4!] of operating potential. The anodes of the two. dischargedevices are connected through respective.resistances/i2 and 43 to a positive tor-- initiale on source4ii; The anode of device 35 isfconnected throughcondenser 1 5 to the control electrode of ZdischargeHdeViCe'SG, which in turn is connected tothe cathode through adjustable resistance 46.

I .jc rrent normally vflowsthrough.the right-hand discharge device 36 Qandresistance 31. The voltage 'producedo'n resistance 37 by this current is su flicient to drive. he left-hand cathode suffi'cientlypos'itivewith respect tofgrid 34 to prevent the flow of currenti'n device. 35. Thus, the anode of this devicelis at a high positive potential. SinceQthe grid offdevi 36 is at cathode potential, condenser .45. is normally charged.-

..When .a positive pulse, .indicated at 33,. is supplied ;to1.g"rid. 3'4, devi'cejl35 becomes conducting and its anode potential' drops, Since the charge in condenser 45. does not, change rapidly, the grid of devicetfi is.driven negatively'thereby inter.- rupting. the current in. device 36. {This condition remains, however, only until the charge. on condenser '45 leaks on to'a su'fficient extent to permit current again .tostart its flowindeyiceifi. When this happensjthe potential "developed across resistor 31 drives the left h'and ca'thodesulficiently positive with lrespect to grid 1351 120 reducethe current indischargegdevice 35, the.ati0i'l being, of course. accumulative luntill static conditions are reached,. v v her eir1 delgice 35fi f rnpletely nonconducting .anddevicefli is eonductingits normal amountof'current.

\ In this ,Way the multi vibrator 21p'roduces. on resistance., l3, a pulse wave such as, that indicated at- ,48, this wave having positive pulses 49 of a duration equal to. approximately 3 /2% 2 of the period. of the pulse wave. The duration of these positive pulses is adjustable .toa certai extent by a variation of resistance 36. 1 Device .28 operates an arnplifier andclipper of these pulses. I ts cathode is connected to the point 38 andf its anode is connected through resistance 5| tofthe point-14, ltsccntrol electrode isconnected-through resistance 52 to .a point on source 39 sufliciently negative with respect to the cathode to prevent'the flow of or rrent therein. A

parasitic resistance 5311s connected in the grid circuit to prevent undesired parasiticeffects.

Thelwave 48 is supplied to the control electrode joffdeyicejzt through coupling condenser 54 and is reproduced upon the primary of transformer 5% the fort indicated "at. 55,, the .wavc 55 comprising negative pulses of squarewave shape. The

secondary Winding of transformer 56 is connected between the control electrodes of devices 29 and 30, which are connected together, and a negative point on the source 39. The anodes of devices 29 and 39 are connected together and through resistance filan d lamp :1 to the positive terminal of the source-.40.; Preferably; the source all is one of about 2,000 volts thereby placing a high positive potential on the anodes of devices 29 and 33, the cathodes of which are connected to point 38. The screen grids of these devices are connected together and to the point 46.

These devices 29 and 36 are preferably of high current carrying capacity to pass large current through the lamp 4 during the pulse periods. Parasitic resistances 53 are included in each of the g'rid leads andfurther parasitic resistances 59 are connected in each of the anode leads.

Transformer 5% is of such design that the pulse wave ES is reproduced on the secondary winding in the'f'orm indicated at 63 comprising positive pulses of square wave shape and of the same duration as the pulses of wave '48. These pulses overcome the highnegative bias on these grids provided by source 33which'rnay beof 400 volts and cause devices scans 30' 'topas's current to Practically the full extent oftheir cathode emission thereby passing large current through re- 'sistance 57 and tne lamp 4. Thus, the lamp 4 produces "an intense light pulse of theduratio n of the positive pulses of the Wave 33 produced by the rnulti-vibrator,"these pulses, of course, illurninatfing the fili'n at aperture 3 andthephotosensitive surface "I It is desired that these light pulses fall upon the photosensitive-areal I! ate, time when the cathode ray is interrupted or blanked 'ou't. Preferaloly-this light falls upon the'screen'during the blanking period; or retrace interval, of the verti'c'al sweep'produc'ed-by the'vertic'alsweep generator24. 'That is,'the ray isdeflected gradually downward ove'r thearea I during the line s'cannin'g produced by the horizontal sweep generator 22'. It is'then blankedout, crinterruptd, and returned to the starting point. The light'pulse isproduced during this interval when the cathode ray is blanked out. The cathode ray is interrupted during this time by means ofa-pu'lse supplied to control electrode 64 of the cathode ray tubeby means of a blanking pulse generator 65 synchronized "over conductor 31 from the synchronizing pulsegenerator 25.

This blank interval may have a duration of from 5 to 8 per cent ofthe vertical 'scanning'pe- :riod which is /60 of a second. The positive pulses ;of the wave 33 which occur during thisinterval may havea duration-of about 5% of the vertical sweep period. The positive pulses "of the Wave 48 produced by. the multi-vibrator have a duration fonly 3 /2% .of this period, the duration ofthese pulses being-adjustable-by variation of resistance 36 to maintain the pulses of light entirely within .the'blanking interval of =thevertical sweep so that the photo-sensitive area I! is not illuminated .duringany portion of. its scanningperiod. l'Ihe se light pulses of course occur only when the film is stationary in aperture 3, the pulse equipment 35, 36,.28, 29, 30 being synchronized jforthatpurpose with the intermittent drive 7 through source 2! .and synchronous motor -8. Duri'ng this interval, 'when-light.falls on the elemental areas offthe. surface ;l1.,..'the elemental areas becomecharged to a degree dependent upon the intensity of thelight fallingpntheirespective elemental areas,thi's, of coursefloeing dependent upon the photographic density of the film at aperture 3 and thus varyin over the photo-sensitive area in accord with the picture to be transmitted. These charges are retained by the respective elemental areas of the surface [1 until the cathode ray impinges thereon during the l ne scanning when such areas are discharged, this producing corresponding current in resistance I9. This line scanning reconditions the area for recharging during the next vertical blanking or retrace interval at which time source 4 produces another intense flash of light in accordance with wave 63.

- Commonly in the past the light falling upon the area I! has been interrupted mechanically by means of shutters operated in synchronism with the film drive mechanism and. with the vertical sweep of the cathode ray tube. It has been f0und,however, that my invention not only has the advantage that it obviates the use of the mechanical shutters and the synchronizing mechanism therefore, but it affords means whereby the light pulses impinging on the area I! may have far greater energy content than it was practicable to produce by means of a system employing mechanical shutters. This is because the time required for operation of the shutters is such that ordinarily they'cannot be fully opened and closed quickly enough to permit transmission therethrough of a large portion of the light generated by aconventional light source. Moreover, since the conventional source of light is operated continuously, it was necessarily operated at lower intensity than is practical when intermittent operation is employed. In my invention the current passed by the lamp is about ten times greater than could be passed continuously thereby producing pulses of far greater intensity than could be obtained were the lamps operated continuously.

In my system not only may the light source be of greater intensity than would be practical were it continuously operated but the light pulses being substantially rectangular have substantially their full intensity during the entire duration thereof.

That is, the light pulses are both initiated and terminated substantially instantaneously. Moreover, the light pulses produced by my system may be substantially longer relative to the vertical blanking or retrace interval than is practical with the operation of mechanical shutters. Such shutters, being operated by a synchronous motor operating under variating conditions of load, line voltage, etc., are subject to some variation in phase of operation relative to the blanking interval and therefore the pulses produced thereby must be made shorter to assure that no part thereof occurs outside of the blanking interval. This diificulty is increased by any looseness in synchronization between generator 25 and the voltage of line 2|. This diniculty is largely eliminated by my invention.

Preferably the lamp 4 is one of the mercury vapor capillary type such as is schematically indicated in Fig. 2. This lamp comprises a thick walled quartz tube 6| having capillary 66 extending between electrode 61 and 58, the latter being adapted to be received in suitable circuit terminals. Within the capillary F6 are two globules of mercury 69 producing vapor which may be ionized by current flowing between electrodes 61 and 68.

It has been found that for best operation of the lamp the vapor in the capillary 66 should be maintained in an ionized condition between the pulses of current controlled by devices 29 and 30.

Such continuous ionization is effected by means of a high resistance 10 connected between negative terminal 38 ,of thesource .40 and a suitable point on the anode circuit of devices 29 and 30 as for example the upper terminal of resistance 51'.

This resistance 10 may have a valueof, for example, 5 megohms or such that a continuous cur-- rent of approximately 0.4 milliampere flows inthe lamp between the pulses. This current keeps the vapor ionized at all times and eliminates irregularity in the starting, or striking, of the arcwhen the devices 29 and 39 become conducting during the positive voltage pulses supplied to the grids thereof. Since this current is very small, the light produced by' the pulses is correspondingly'small and has no adverse effect upon the photo-sensitive area ll during the line scanning.

It has also been found in the operation of the system that the heat generated in the lamp 4 by passage of current therethrough generally is in:- sufiicient to produce'the greatest amount of light from the lamp and that more satisfactory operation is had by supplying additional heat to the lamp,- and particularly to the electrodes Bland 68 thereof. This is effected by means of a heater 12 indicated in Fig. 1 adjacent lamp 4, this heater being connected across a secondary winding of a transformer T3. The primary winding-is connected through a movable tap 16 across a variable portion of an auto-transformer 14 which is excited from the powersource 2 l. Y

Preferably the heater [2 is of the form indicated in Fig. 2 comprising a strip of resistance metal such as Nichrorne extendin parallel withthe lamp and which isv crimped or folded at the regions '55 near the electrodes .61 and 68 thereby to produce more heating of these electrodes than is produced in the portion of the lampbetween theelectrodes. 7

The current flowin in the gas within the discharge device is sufficient to produce adequate heating between these electrodes 61 and 68 but excess heat produced in this region by strip I2 is unobjectionable.

Alternatively I have found that the operation of the lamp may be greatly improved by blowing heated air across the lamp, as by means of a fan, although even with such means it is preferable that the heat be concentrated upon the electrodes more than upon the portion of the lamp between the electrodes.

The proper amount of heating of the lamp greatly increases the light produced thereby during the current pulses supplied thereto by the apparatus above described.

While I have shown a particular embodiment of my invention, it will, 01 course, be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentalities employed, may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in a motion picture television projection system, of a cathode ray camera tube having a photo-sensitive area, means to deflect the ray of said tube across said area in two directions at different frequencies, means to blank said ray during the retrace interval of its deflection at the lower of said difierent frequencies, a motion picture film drive, a gaseous discharge lamp arranged to project light through the film driven by said drive on said area, means comprising a synchronizable pulse generator tmgenerat'e shdr tllperiodic controhpmseset said lower freq'tie'ncmanfearis to s'yiiohwniae'bo'tlisaid pulse :gen orator and KsaiH bIa IikihgmeanS'withsaid 'film drive," energy supply means controlled by said aise geirerator to pass current pulsesof high intensity through'said :lalrnp synchronously with said coiitrol 'pulses, and means to adjust the duration or 's'a-id *contr'oi" uises'withirespeot to said blankin interval. a

2." The combination, in a motion-picture televisibhqardjejotion s'ystem, of a-"ca thode my camera tribe; having a photo-sensitive area, means to defififlthe ray-of 'sa'i'd tube'across s'a'id area in two iiir'e'dtibri's at different frequencies, means to blank siid' ra'y'diiring the retr'aoe iriterval' at the lower of said frequenoie's'i an'iiiterinittent motion pictarel film 'd-ri've-driven by synchronous motor, ari alternatiri'g voltage supply for said motor, a discharge lamp arranged to'projeot-light through the filhi ariven-rysam film drive on said sensitive area eans 'oorhprisihg a syri'chronizable pulse or toger era'te 'short'periodic control pulses at sai'd' i'ower fr equeny, means to synchronize bothsai'd' pulse generator and said :bla'n'king' means wlth -said filin drive energ y supply means 'contriilletl by'kaid puise'generator to supply an intense iciulse-cfi efiergy t'o said lainp in synchronism with "earn orsaid'boritroi pulses, and means to adjii'st th diiration'iif "'sai ld -dohtrol pulses with respect to the duratioii of saidre'trace' interval. -3IThe' fitfiflbi'ii'aifiifin," "a motion picture tele- Vision rojection sy st'em, of a cathode ray camera tfibe 'l'ia vinfi a photo se'ns'itive areafdeflec'tion htaris' therefor, a matron picture projector comprising a smears mechanism and a projection iamp' arranged to throw light on said area, a tfifiltfvibr'a'tor; means to synchronize sa'id'multivibrator and said mechanism with said-deflection means, and m'eans'eontrolled by said gmltivibmtor to pass intense current pulses through said lamp ha ving .durationshortrelative to the periodof said-multivibrator.

, 4.. The .oorn b nation, in .a motion picture television projection system, -o facathode raytcamera tube having :a .photo sensitive area, deflection means to-defiect the ray across said area in two directions at difierent irequencies, means to'blank said-ray during its retraceeinterval atf'the lower of .said ,frequencies, a. motion picture projector comprising afilm drive mephamsm and a projection lamp arranged to project light on said area,-

4 REFERENCES, CITED The following references are .of record inxthe file of this patent:

STATEfi PATENTS Number Name 7 Date Newhouse -Apr;;9,, 1918 Hoxie Novr8, 1927 Spaeth .*Sept.--6, I932 Edgerton Jan: 9, 194!) 7 Seeley D6091; I942 FOREIGN PATENTS Country 7 Date Australias Dec, 3, 1935 France Feb, 20,1935 Great Britain-n .Mar. 10,1939 GreatBritain June], 1939 ,France July,3. 1939 Number 

